Biology 2581B Study Guide - Quiz Guide: Limb Bud, Internal Capsule, Body Plan
1 Jun 2020
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A limb is an appendage to the basic body plan - eg legs. Invertebrates tend to have lots of these appendages. Most vertebrates, like us, can be described as tetrapods because they have 4 limbs, but there are exceptions to this - snakes are vertebrates with no limbs, for example. The initial formation of a limb bud occurs relatively early on in development - in chicks, limb buds start to appear at day 3 in the form of small swellings with an apical ectodermal ridge along the outside edge. The site of limb bud formation along the ap axis is determined by hox genes due to their importance in conferring segmental identity. An example of these genes is hoxb5 in mice. If you knock this out you get a homeotic transformation in which the forelimbs develop at a more anterior level in a different segment. This does not necessarily mean that these hox genes cause limb buds to grow directly.
